Electric heater



Feb;26, 1935. l i. TROMBETTA UAL 1,992,588

' ELECTRIC HEATER Filed Nov. l, 1929 @Hillel-l Patented Feb. 26, 1935 UNITED STATES- VPivrsivr orties ELEc'rmc HEATER Panflo Trombetta and George W. Knight, Milwaukee, Wis., assignors, by mesne assignments,

to Allen-Bradley Company,

Milwaukee, Wis., a

5 Claims.

This invention relates to electric heaters.

An object of the invention is to provide an electricheater having heat characteristics which are controllable over a wide range.

The electric heater to which the invention applies is particularly adapted for use in thermally operable circuit breakers such as that disclosed in the copending application of Gustav O. Wilms and Paniilo Trombetta filed on even date herewith. This circuit breaker is ordinarily employed to protect electric motors and has its heater connected in circuit with the motor to generate heat and soften a 4fusible binder to permit the circuit breaker to open whenever the motor is subjected to an excessive overload' or whenever a predetermined overload continues for a predetermined period of time.

.im overload which would damage one motor might not damage another as the period during which motor may be operated saiely under an overload varies according to the characteristics oi the motor and the arnount of overload.

liiractically all motors may be operated safely under small overloads for long periods ci time, operated under large overloads for periods of time l which vary according to the amount oi overload,

but are cuicirly damaged by an excessive overload.

in order to obtain the maximum output during a given period of time,` a motor should continue to operate until subjected to a prohibitive overload` or until an overload has continued for such a length ci time that further operation would result in damage to the motor.

Motors which aresubjected to overloads may be protected by thermally operable circuit breakers.

Another object of this invention is to provide such a circuit breaker with an electric heater having heat characteristics corresponding to the characteristics of any particular rnotor.

In the past, diiculty has been experienced in providing, lin a circuit breaker of the type shown in the present application, a heater made of resistance material having a uniform cross-section, the heat characteristics of which varied only Within close limits.

Another object is to provide an electric heater made of resistance material of non-uniform cross-sectional area whereby the heat characteristics thereof may bel varied within close limits.

Under a slight overload, the'heater of a thermally operable circuit breaker generates heat which will accumulate and soften the fusible binder unless a portion of the heat is dissipated.

Another object is to provide an electric heater havingA a radiator to dissipate a portion of the heat generated thereby.

Another object is to provide an electric heater in which the path of the current is constricted 5 at the point of eiiective heat distribution.

Another `object is to provide an electric heater made from a flat strip of resistance material and having a constricted part to impede the flow of an excessive current therethrough and a radiator to dissipate a part of the heat generated the constricted Another object is to provide an electric heater which may he ac'lapted for use in various circuit breakers and to protect various 'types and sizes ci motors.

Another ohiect is to provide an electric heater roede roro. a 'flat strip ci resistance material and shaped to denne and partially enclose a heating space. f do Another object is to provide an electric heater vri'iich be readily and economically manniactured.

According to the invention, the heater is made irons fiat strip of resistance material, provided with terminals. ior connection into an electric circuit, constricted intermediate the terminals tccurrent iiovring there- "f provides a radiator in.- ill ediate the constricted art and a terminal to dissipate ci the generated.

Embodirnents of the invention and a circuit breaker 'which the saisie :may be employed are shown in the accompanying drawing, in which the views are as follows:

Fig. l is a top plan view of the circuit breaker, the top cover plate being omitted.

Fig. 2 is a sectional iront view thereof taken on the line 2-2 oi Fig. l. 40

Fig. 3 is a perspective View oi" the heater shown in Fig. l. Y

Fig. 4 is a perspective view of a modification of the heater shovvn in Fig. 3.

Figs. 5 and o are perspective views of other forms of heaters. l

The circuit breaker has its mechanism arranged in and' carried by a casing Il which is preferably made of insulating material and has the top and bottom thereof closed by cover plates 2. 5l)

A support 3 is pivoted upon a pin l and carries contacts 5 and t to engage contacts "l and 8 which are electrically connected to terminals 9 and l0 arranged upon the outside of the casing l for connection into an electric circuit.

The contact 5 is in continual engagement with the spring contact 7 which tends to swing the support 3 upon the pin 4 and move the contact 6 outv of engagement with contact 8 to open the circuit.

A ratchet wheel 11 is fixed by a fusible binder on a vheat conductor 13 which is carried by and heat insulated from the support 3.

'I'he contact, 6 is held in engagement with the contact 8 by a catch 14 which is carried by the casing and engages the ratchet Wheel 1l.

'I'he circuit breaker described above forms no part of the present invention and is described and claimed in the copending application of Gustav O. Wilms and Panfilo Trombetta.

An electric kheater' 15, which Iembodies the present invention, is connected between the contacts 5 and 6 and arranged in intimate thermal association with the heat conductor 13 to generate heat upon the passage of an excessive current through the circuit breaker.

The heat is transferred to the heat conductor 13 by radiation and conducted thereby to the binder 12 to soften the same and release the ratchet Wheel so that the springv contact 'I may urge the support 3y upwardly and separate contacts 6 and 8 to open the circuit.

'I'he electric heater 15 is formed from a flat strip of resistance material, bent intermediate its ends to form a heating compartment 16, and provided with terminal apertures 17 and 18 to receive the screws 19 and 20 by means of which the heater is connected between the contacts 5 and 6.

An aperture 21, of greater diameter than the conductor 13, is formed in the heater 15 intermediate the ends thereof, and the conductor 13 extends therethrough and into the compartment 16.

The current carried by the heater 15 is forced through the constricted parts 22 at each side of the aperture 21 and any current above a predetermined minimum will cause the same to become high temperature areas which radiate heat to the heat conductor 13.

A part of the heat generated in the high temperature areas 22 is conducted to and radiated by the side walls 23 of the compartment 16 and the terminal arms 24.

The side walls 23 also conne a part of the heat in thecompartment 16 to heat that part of the conductor 13 lying therein and prevent excessive radiation therefrom.

The heat generated in the high temperature areas 22 under the influence of a small or harmless overload Will be largely dissipated by the radiators 23 and 24.and the amount of heat conducted by the conductor 13 to the fusible binder 12 will be insuiiicient to fuse the same.

The motor may thus continue to operate under the small and harmless overload.

A certain amount of the heat generated by larger overloads is dissipated by the radiators 23 and 24 but conduction of heat by the conduc tor 13 exceeds the dissipation by radiation according to the overload, so that the binder 12 is fused after certain periods of 'time which vary inversely to the amount of overload.

A properly selected heater arranged in the circuit breaker which controls the motor will permit the motor to continue operating until the overload becomes dangerous.

A large and prohibitive overload causes a high degree of heat to be generated and transferred to the fusible binder 12 to fuse the same almost Lacasse instantly as the radiators 23and 24 are incapable of instantly dissipating so large an amount of heat.

The heat characteristics of the heater may be varied vto correspond to the characteristics of any motor or other appliance by varying either the width or thickness of the resistance material, varying the size of the aperture 21 relatively to the diameter of the heat conductor 13 to vary the distance that heat must be radiated to the heat conductor, varying the diameter of the aperture 21 relatively to the width oi the strip to vary the cross-sectional area of the high temperature areas 22, varying the size of the radiators 23 and 24 to vary the area of the radiating surfaces, varying the width of the strip contiguous to the aperture 21, or providing fins to increase the radiating surface as shown in Fig. 5, varying the width of the compartment 16 to vary the distance between the heat conductor 13 and the radiators 23, varying the depth of the compartment 16 to vary the indirect heating areas and the heat dissipating surfaces, or by combining any two or more of such variables.

The heater shown in Fig. 4'is similar to the heater 15 except that one side wall thereof is provided with a reverse bend 25 having apertures 26 and 2'? therein in alinement with the aperture 21.

Additional high temperature areas 22 are thus provided which multiply the capacity of the heater.

The heater shown in Fig. 5 is made from a flat strip of resistance material and reduced in Width intermediate the ends thereof to form a high temperature area 28 and radiators 29.

The high temperature area 28 may be looped to form a heating compartment 30 to receive a heat conductor 13 or the binder to be fused.

The heater shown in Fig. 6 is similar to the heater shown in Figs. 2 and 3 but has a notch 31 formed at each side of the aperture 21 to reduce the width of the high temperature areas 22 and may also be provided with fins 32 to increase the area of the radiators 24.

The heaters shown in Figs. 5 andl 6 may be shaped to conform to the instrument in which the same are employed and the heat characteristics thereof may be varied as above set forth.

The invention disclosed herein is susceptible of various modifications and adaptations without departing from the scope thereof as hereafter claimed.

The invention is hereby claimed as follows:

1. An electric heater for heating a heat conductor, comprising a high resistance metal strip provided with a convoluted part intermediate its ends and apertures in said convoluted part in axial alinement for receiving said heat conductor, and terminals arranged at opposite sides of said convoluted part for connecting said heater in an 'electric circuit.

2. An electric heater for heating a heat conductor, comprising a high resistance metal strip provided with an aperture formed therein intermediate its edges to receive said heat conductor and restricted parts of high impedance to electric current between said aperture and said edges for generating heat, having the parts of said strip at opposite sides of said aperture bent to parallel relation providing opposed radiating surfaces which denne and partially enclose a heating space for said conductor, and having terminal parts extending from said radiating parts for connecting said heater into an electric circuit.

3. An electric heater for a thermally operable circuit breaker having a heat conductor extending therefrom, comprising a high resistance ilat metal strip provided withan aperture formed therein intermediate the edges thereof to receive said extending heat conductor and to provide restricted parts between said aperture and the edges of said strip for impeding the flow of electric current therethrough to generate heat and having parts of said strip at opposite sides of said aperture'arranged to deiine a heating space for vsaid heat conductor and other parts of said strip bent outward from said latter parts toprovide terminal connections -for connecting said heater into an electric circuit and for supporting said- Vheater on said circuit breaker.

4. A circuit breaker including a heat con" ductor and a latch connected to said heat conductor bya fusible'binder, a heating unit comprising a metallic strip having an aperture therein surrounding said heat conductor at the end thereof adjacent said latch, radiating ns formed integrally on said strip on either side of said aperture and extending substantially parallel to said conductor to deilne and Apartially enclose a heating space, and terminal members on said strip to connect the heating unit'in a circuit.

5. In a circuit breaker including a heat conductor and a latch connected to said heat conductor by a fusible binder, a heating unit comprising a metallic strip having an aperture therein surrounding said heat conductor at the end thereof adjacent said latch, radiating tins formed PANFrLo momma. ,0

GEORGE W. KNIGHT. 

